(1) Field of the Invention
This invention relates to turbomachinery, and more particularly to cooled turbine blades.
(2) Description of the Related Art
Heat management is an important consideration in the engineering and manufacture of turbine blades. Blades are commonly formed with a cooling passageway network. A typical network receives cooling air through the blade platform. The cooling air is passed through convoluted paths through the airfoil, with at least a portion exiting the blade through apertures in the airfoil. These apertures may include holes (e.g., xe2x80x9cfilm holesxe2x80x9d distributed along the pressure and suction side surfaces of the airfoil and holes at junctions of those surfaces at leading and trailing edges. Additional apertures may be located at the blade tip. In common manufacturing techniques, a principal portion of the blade is formed by a casting and machining process. During the casting process a sacrificial core is utilized to form at least main portions of the cooling passageway network. Proper support of the core at the blade tip is associated with portions of the core protruding through tip portions of the casting and leaving associated holes when the core is removed. Accordingly, it is known to form the casting with a tip pocket into which a plate may be inserted to at least partially obstruct the holes left by the core. This permits a tailoring of the volume and distribution of flow through the tip to achieve desired performance. Examples of such constructions are seen in U.S. Pat. Nos. 3,533,712, 3,885,886, 3,982,851, 4,010,531, 4,073,599 and 5,564,902. In a number of such blades, the plate is subflush within the casting tip pocket to leave a blade tip pocket or plenum.
One aspect of the invention involves a blade having a platform and an airfoil with a root at the platform and a tip. The airfoil has leading and trailing edges and an internal cooling passageway network including at least one trailing edge cavity. Trailing edge holes extend from the trailing edge to the trailing edge cavity. Tip holes extend from the tip to the trailing edge cavity.
In various implementations, the tip holes and a distal group of the trailing edge holes may be outwardly diverging from the trailing edge cavity. The tip holes may be of circular cross section and may have a diameter between 0.3 and 2.0 mm. Each of the tip holes may have a circular cylindrical surface of a length at least five times longer than a diameter. There may be between two and six such tip holes. Each of the tip holes may extend through a casting of the blade. The blade may have a body and a tip insert and may have a tip plenum in communication with the cooling passageway network. The plenum may be bounded by a wall portion of the casting along pressure and suction sides of the airfoil and by an outboard surface of the tip insert subflush to a rim of the wall portion. The wall portion may be uninterrupted along a trailing portion of the plenum spanning the pressure and suction sides. The tip may have a relieved area along the pressure side. The relieved area may extend partially across openings of the tip holes.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.